OBJECTIVES: 1) To determine the anaerobic microbial inhabitants of the cockroach gut. 2) To determine what organisms are attached to the gut wall. 3) To study the factors involved in the pleomorphism of Fusobacterium varium, an anaerobic isolate from the roach gut. METHODS: 1) Isolation of anaerobic organisms by the Hungate technique and the anaerobic chamber. 2) Localize organisms by specific antibody-EM techniques. 3) Analytical identification of a factor(s) from yeast extract responsible for pleomorphism of F. varium.